The reason I say the drag-free drift must be short when nymphing on tight line without an indicator is this: After the tuck cast is made the fly, let's say, is below the end of the line. (The leader is certainly not straight, but perhaps curved backwards.) We then retrieve the line at the speed of the current. (By the way, if we get a strike soon after the fly enters the water and sinks to the bottom, how will we feel the strike as the leader isn't tight?)

As we retrieve more line the leader begins to straighten. If we have a 9-foot leader, for example, it will probably completely straighten after we retrieve no more than five feet of fly line. Once the leader is straight and we are retrieving at the speed of the surface current we have drag, don't we?

On the other hand, if we're using and indicator and make a pile or wiggle cast and have slack in the line and in the leader, and we then retrieve at the speed of the surface current, the slack, I would imagine, allows for a longer drag-free drift. (Granted, the slack might prevent us from detecting a strike.)